Pad wear indicator and pad wear indicator probe

Abstract: A brake pad wear probe contains a plurality of terminals turned or bent into a U-shape with their tip positions offset from each other. The terminals are cut in stages according to the wear development degree of the brake pad. The terminals define energization routes to electro-magnetic coils at relays, and the broken line state of the terminal can be detected at the respective relay by detection of a break in its corresponding energization route. As a result, electro-magnetic switches work in response to the wear development degree, turning on predetermined indicator lamps of a display to inform a driver of the brake wear condition.

Description: BACKGROUND OF THE INVENTION This invention relates to a pad wear indicator for informing the user of brake pad wear and more particularly to a pad wear indicator for informing the user of brake pad wear in response to the broken line state of an electric wire path disposed in a pad wear indicator probe wearing together with a brake pad. A pad wear indicator comprises a pad wear indicator probe containing a U-shaped electric wire path that is broken when the probe wears together with its corresponding brake pad and includes a pad wear indicator display for detecting the broken line state of the electric wire path for displaying the wear state of the brake pad. Figures 10 and 11 show, respectively, a conventional pad wear indicator probe and a corresponding conventional pad wear indicator display. To form the pad wear indicator probe 1, a copper wire 3 having barrel parts 2 that can be crimped onto electric wires formed at both ends is formed into a U-like shape, and the barrel parts 2 are crimped onto a pair of electric wires 4 whose tips are coated. The entire assembly is molded in resin. The U-shaped turn part is directed toward the brake disk side for use as a brake pad. The pad wear indicator display 5 (Fig. 11) comprises a relay 7 having an electro-magnetic coil 6 in series with the pad wear probe 1 that is connected to a power line. An indicator lamp 9 in series with an electro-magnetic switch 8 of the relay 7 is also connected to the power line. The electro-magnetic switch 8 is turned off when the electro-magnetic coil 6 is energized. With this construction, the copper wire 3, located within the pad wear probe 1, initially supplies power to the electro-magnetic coil of the relay 7 via the electric wire 4 and the copper wire 3 (Figure 11). Therefore, the electro-magnetic switch 8 is turned off as shown with the broken line, and the indicator lamp 9 cannot be energized. As a brake is used, the lining of its brake pad wears along with the pad wear probe 1. When the probe wears a predetermined amount from the tip, the turn part or bend of the copper wire 3 in the pad wear probe 1 wears until it is eventually cut, thus opening the circuit. Then, the energization path to the electro-magnetic coil 6 is broken, and thus, the electro-magnetic coil 6 becomes deenergized, turning on the electro-magnetic switch 8, as shown with a solid line in Figure 11. Accordingly, the indicator lamp 9 is energized, prompting the user to replace the brake pad. When the conventional pad wear indicator described above has worn by a preset amount, it suddenly prompts the user to replace the brake pad without much warning. Since the remaining amount in which the user is to be prompted to replace the brake pad is made the minimum value, he or she, upon being suddenly prompted to replace the brake, may lack sufficient time to do so. If the lamp goes on during running, he or she may panic or lose his or her peace of mind. While the setup remaining amount of the lining could be increased to avoid panic by allowing the car operator adequate time in which to replace the brake pad, premature indication of a worn brake pad is wasteful. Prior art documents EP-A-0 464 347, EP-A-0 465 954, DE-A-3 007 887 and DE-A-2 311 197, respectively, disclose a brake pad wear indicator probe according to the preambles of claims 1 and 3 containing a plurality of U-shaped electric wire paths that are directed toward a tip of said probe, said plurality of electric wire paths being operatively engaged with a brake pad and wearing together with the brake pad, said plurality of electric wire paths being different in length between the turn part and the tip of the probe and brake pad. SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a pad wear indicator that can inform the user of accurate replacement time of a brake pad without his or her feeling a sense of unease or panic. Another object of the invention is to provide a brake wear indicator that maximizes the life and usefulness of each brake pad. These objects of the present invention are solved by a brake pad wear indicator probe and a brake pad wear indicator according to claims 1 and 3 and claims 4 and 6, respectively. According to the invention the wear amount of a brake pad is displayed in stages, so that the user can know the wear condition before the brake pad needs to be replaced due to wear and can reduce the chances of panic or feeling a sense of unease at sudden notice. Since the user is informed of the wear condition as it progresses, the maximum wear amount can also be set for finally prompting the user to replace the brake pad for using resources effectively, thus extending the service life of the brake pad. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in detail with reference to the following drawings, wherein: Figure 1 is a perspective view for explaining the general structure of a pad wear indicator probe; Figure 2 is a top view of a terminal part in the probe in Figure 1; Figure 3 is a schematic block diagram of a pad wear indicator; Figure 4 is a front view of the indicator; Figure 5 is a perspective view showing a pad wear indicator probe according to a first embodiment of the invention; Figure 6 is a perspective view of the assembled pad wear indicator probe according to the first embodiment of the invention; Figure 7 is a perspective view of a pad wear indicator probe according to a second embodiment of the invention; Figure 8 is a perspective view of a pad wear indicator probe being no embodiment of the invention; Figure 9 is a schematic block diagram of a pad wear indicator using the pad wear indicator probe of Figure 8; Figure 10 is a perspective view of a conventional pad wear indicator probe; and Figure 11 is a schematic block diagram of a conventional pad wear indicator. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 is a perspective view for explaining the general structure of a pad wear indicator probe (hereinafter probe). Figure 2 is a top view of an electric wire path in the probe. In Figures 1 and 2, a terminal 11 is formed to define an electric wire path and is turned substantially into a U shape. The terminal 11 includes a broken line part 11a projecting toward a tip at the part of the wire including a bend or turn. A pair of barrel parts, each designated as 11b, are crimped onto respective ones of a pair of electric wires 12 at rear ends thereof. The two terminals 11 are overlaid so as not to contact with each other and are offset and positioned so that they differ slightly in tip position of broken line part 11a. The probe 10 is molded in resin. If the tip of the probe 10 is located on the side where the broken line 11a at the terminal 11 is disposed, the electric wire path defined by the terminal 11 whose broken line part 11a is closer to the tip is assumed to be a first detection part S1, and the electric wire path defined by the terminal 11 whose broken line part 11a is furthest from the tip is assumed to be a second detection part S2. In this probe, the two terminals 11 have a similar shape and are offset from each other. The probe, however, is not necessarily limited thereto, and terminals 11 having different lengths can also be provided and used in such a manner that the positions of broken line parts 11a are not aligned. The probe 10 is held to a brake pad with the tip of the probe 10 directed toward a brake disk for each wheel. As shown in Figure 3, the electric wires 12 in the first detection parts S1 of the probes 10 are also connected in series, and the electric wires 12 in the second detection parts S2 of the probes 10 are connected in a separate series. Each series circuit has one end grounded and the other end connected to one end of an electro-magnetic coil in relay SW1 or SW2. The electro-magnetic coil has the other end connected to a positive power supply. Electro-magnetic switches in the relays SW1 and SW2 are connected in series with indicator lamps L1 and L2 respectively, one end being grounded and the other end being connected to a positive power supply. Neither electro-magnetic switch conducts when its corresponding electro-magnetic coil is energized. The indicator lamps L1 and L2 are housed in an indicator 20 disposed in a car. As shown in Figure 4, the indicator 20 comprises two light transmission lenses or similar illuminating devices 21 with characters "1/2" and "EXCHANGE" (or other descriptive words to indicate a driver of the stage of brake wear) on their surfaces. The indicator lamps L1 and L2 are disposed on the rear surfaces thereof. Here the relays SW1 and SW2 and the indicator 20 make up a pad wear indicator display. The operation will now be described. When the probes 10 are first installed, they have not worn at all, and all terminals 11 form U-shaped electric wire paths. Therefore, both electric wire paths of the first series of detection parts S1 and the second series of detection parts S2 conduct, and the electro-magnetic coils of the relays SW1 and SW2 in series with the electric wire paths are energized from the positive power supply. Since the electro-magnetic coils are energized and excited, the electro-magnetic switches of the relays SW1 and SW2 become nonconducting, and the indicators L1 and L2 are not energized and remain off. This condition corresponds to the broken line position of the switch in Figure 3. Therefore, the indicator 20 displays nothing, and the driver can recognize that little or no wear has occurred on the brake pads. As the driver uses the brake, the brake pad wears, and thus, the probe 10 also approaches the brake disk and gradually wears from its tip portion. In the beginning of wearing the probe 10, only the mold part of resin wears, but as the brake pad wear develops, the resin of the probe 10 is gradually shaved off completely. The broken line part 11a of the first detection part S1 having the broken line part 11a near to the tip of the probe 10 starts to expose gradually, and the brake eventually contacts and completely shaves broken line part 11a. If the broken line part 11a of the first detection part S1 is shaven away at any one of the four wheels, the series wire path grounded via the electro-magnetic coil of the relay SW1 from the positive power supply becomes nonconducting, and the electro-magnetic coil becomes deenergized, thereby causing the electro-magnetic switch of the relay SW1 to conduct for energizing and turning on the indicator lamp L1 (the solid line position of switch SW1 in Figure 3). As a result, the lamp of the indicator 20 emits light on the rear of the light transmission lens 21 on which "1/2" is displayed. From the indicator lamp, the driver can recognize that the brake pad has worn although it need not be replaced immediately. In this case, the driver, who need not replace the brake pad immediately, does not feel the need to panic or a sense of unease. The driver may request servicing at a convenient and predetermined replacement time. If the driver cannot replace the brake pad and continues to use it, the broken line part 11a of the second detection part S2 also starts to expose, contacts the brake disk and is eventually shaven. If the broken line part 11a of the second detection part S2 is shaven away at any one of the four wheels, as with the first detection part S1, the series wire path grounded via the electro-magnetic coil of the relay SW2 from the positive power supply no longer conducts, and the electro-magnetic coil is no longer energized, thereby causing the electro-magnetic switch of the relay SW2 to conduct for energizing and turning on the indicator lamp L2 (the solid line position of SW2 in Figure 3). The indicator lamp L1 remains on because the power supply route to the electro-magnetic coil of the relay SW1 remains broken. When the indicator lamp L2 goes on, the lamp on the rear of the light transmission lens 21 on which "EXCHANGE" is written also emits light at the indicator 20. From the illuminated "EXCHANGE" signal, the driver can recognize that wear has developed to an advanced degree, and the time to replace the brake pad is reached as expected. Therefore, the driver may replace the brake pads at the service factory as prompted by this indication. Here, when the second detection part S2 is broken, both indicator lamps L1 and L2 go on at the indicator 20. Other indication schemes are possible. For example, when the electro-magnetic coil of the relay SW2 is no longer energized, and if the power supply route to the indicator lamp L1 is turned off by using another contact of the relay SW2, only one of the indicator lamps L1 or L2 will be made to go on. Because some conventional pad wear indicator displays prompt the driver to replace the brake pad without much warning, some drivers may not recognize the importance of this indicator and will pay no attention to what maybe considered an emergency. Therefore, the driver must be requested to replace the brake pad before it wears completely, which results in premature servicing and waste. According to said indicator, however, when one of the indicator lamps goes on, the driver is informed that the brake pad is close to requiring replacement, and when the second indicator lamp goes on, the driver can recognize the need for immediate replacement. Therefore, the EXCHANGE lamp need not be turned on until the brake pad wears considerably for effective use of resources. Figures 5 and 6 show a probe according to a first embodiment of the invention. In this embodiment, a cylindrical core 13 having the upper part 13a of small diameter and the lower part 13b of large diameter is provided. Separate electric wires 12 are wound around the small-diameter part and the large-diameter part, respectively, and turned and molded in one piece with resin (Fig. 6). With this structure, since each electric wire 12 is wound around the different diameters about upper and lower portions of wire 13, the distance between the turn of one electric wire 12 and the tip of the probe 10 differs from that between the turn of the other electric wire 12 and the tip of the probe 10 by the difference in radius between the small-diameter and large-diameter parts. Therefore, in response to the wear development degree, the electric wire wound around the large-diameter part is first cut, then the electric wire wound around the small-diameter part is cut. Figure 7 shows a probe according to a second embodiment of the invention. In this embodiment, stage parts are formed on the tip side of a resin-molded body 14, and a pair of through holes 14a, 14b are formed from the front end to rear end of each part. Two electric wires each designated by 12 that are turned or bent into a U-shape are inserted into the two pairs of through holes 14a and 14b. With this structure, each electric wire 12 is turned on the respective tips of the stage parts formed on the tip of the resin-molded body 14, and the distance between the turn of one electric wire 12 and the tip of the probe 10 differs from that between the turn of the other electric wire 12 and the tip of the probe 10 by the stage-part difference. Therefore, in response to the wear development degree, the electric wire turned in the higher stage part is first cut, then the electric wire turned in the lower stage part is cut. Figure 8 shows a probe being no embodiment of the invention, and Figure 9 shows the circuit configuration using the probe of Figure 8 for displaying the wear condition. In this probe, a terminal 15 comprises a line path 15a sloping toward the tip and detection line paths 15b1 to 15b3 extending from the front and rear ends and the middle of the slope line path 15a to the rear end of the probe 10. The detection line paths 15bl to 15b3 are crimped onto electric wires 12 and are molded with resin to form the probe in a unitary assembly. The detection line path 15b3 is grounded, and the detection path line 15a is connected to one end of the electro-magnetic coil of relay SW1, and 15b2 is connected to one end of the electro-magnetic coil of relay SW2 (Figure 9). The circuit configuration of the relays SW1 and SW2 and indicator lamps L1 and L2 is similar to that shown in Figure 3. With this structure, because the detection line paths 15b1 and 15b2 are initially connected to the detection line path 15b3 via the slope line path 15a, the electro-magnetic coils at the relays SW1 and SW2 are energized, and the indicator lamps L1 and L2 are not energized. However, as brake pad wear develops, the slope line path 15a is shaven from the tip side gradually, and conduction between the detection line path 15b1 and the slope line path 15a discontinues. As a result, the electro-magnetic coil of the relay SW1 is not energized and the indicator lamp L1 goes on for displaying "1/2" at an indicator 20. As the brake pad wear further develops, conduction between the detection line path 15b2 and the slope line path 15a is also turned off. The electro-magnetic coil of the relay SW2 is not energized, and the indicator lamp L2 goes on for displaying "EXCHANGE" at the indicator 20. While the invention has been described in detail with reference to preferred embodiments thereof various changes may be made without departing from the scope of the invention. For example, although wear development has been described in which two levels of wear are displayed, it is also possible to display wear in more steps using multiple indicator arrays connected to corresponding multiple line paths and displays.

Claims: A brake pad wear indicator probe (10) containing a plurality of U-shaped electric wire paths (12) that are directed toward a tip of said probe (10), said plurality electric wire paths (12) being operatively engaged with a brake pad and wearing together with the brake pad, said plurality of electric wire paths (12) being different in length between the turn part and the tip of the probe and brake pad, characterized in that said plurality of electric wire paths (12) engage with a cylindrical core element (13) having first (13b) and second (13a) diameter portions, said first diameter portion (13b) being larger than said second diameter portion (13a), and one of said wire paths (12) engaging with said first diameter portion and a second of said plurality of wire paths engaging with said second diameter portion. The brake pad wear indicator probe (10) as claimed in claim 1, wherein a second distance from said second diameter portion (13a) to said tip of said probe (10) is greater than a first distance from said first diameter portion (13b) to said tip of said probe (10). A brake pad wear indicator probe (10) containing a plurality of U-shaped electric wire paths (12) that are directed toward a tip of said probe (10), said plurality electric wire paths (12) being operatively engaged with a brake pad and wearing together with the brake pad, said plurality of electric wire paths (12) being different in length between the turn part and the tip of the probe and brake pad, characterized by further comprising a first stage part having a first length and a second stage part having a second length, the first length being greater than the second length, wherein both stage parts are formed on the tip side of a resin-molded body (14), and a pair of through holes (14a; 14b) are formed from the front end to the rear end of each stage part, said electric wires (12) being inserted into the two pairs of through holes (14a; 14b), and wherein one of said plurality of electric wire paths (12) engages with a tip portion of said first stage and another of said plurality of electric wire paths (12) engages with a tip portion of said second stage. A brake pad wear indicator (10,20,SW1,L1,SW2,L2) comprising a probe (10) as claimed in claim 1 or 3, further comprising a first relay switch (SW1) and a first indicator lamp (L1), said first relay switch being switchable between on and off positions, said on position corresponding to a state in which all of said plurality of electric wire paths (12) conduct electricity, said off position corresponds to a state in which a selected one of said plurality of electric wire paths (12) becomes an open circuit as a result of a predetermined amount of brake pad wear to activate said first indicator lamp (L1). The brake pad wear indicator (10,20,SW1,L1,SW2,L2) as claimed in claim 4, further comprising a second switch (SW2) and a second indicator lamp (L2), said second switch being switchable between an on position and an off position, said on position corresponding to a state in which a second selected one of said plurality of electric wire paths (12) hat is distanced a further amount from said tip of said probe (10) than said first selected one of said plurality of electric wire paths (12) is eroded corresponding to brake pad wear to create an open circuit to thereby turn said a second indicator lamp (L2) on, said off position corresponding to a condition in which said second selected one of said plurality of electric wire paths (12) remains in a conducting state. A brake pad wear indicator (10,20,SW1,L1,SW2,L2) comprising a probe (10) as claimed in claim 1 or 3, further comprising a brake pad wear indicator display (20) for signaling a broken line state of each of said plurality of U-shaped electric wire paths (12). A brake pad wear indicator (10,20,SW1,L1,SW2,L2) as claimed in claim 6 for wearing together with a brake pad wherein said display section (20) signals a broken line state of each of the electric wire paths (12) in response to at least two stages of wear of the brake pad.

Inventors: ITO KATSUYA, TAKANASHI HITOSHI, ITO, KATSUYA, TAKANASHI, HITOSHI, ITO, KATSUYA, C/O SUMITOMO WIRING SYST.LTD., TAKANASHI, HITOSHI, C/O SUMITOMO WIRING SYST.LTD.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1994
Main classification: F16D66
IPC codes: F16D66